A High Power-Efficiency Transmission Scheme for Memory Nonlinear Power Amplifiers

[[abstract]]正交分頻多工系統具有高的頻寬效率，且能夠對抗多重路徑衰減干擾的優點；其主要的缺點為具有高的峰值平均功率比 (Peak to Average Power Ratio，PAPR)。由於高的峰值平均功率比，使得經過功率放大器(Power Amplifier，PA)的信號，受到放大器操作點的影響而被截掉，引起失真。基頻預扭器 (Predistorter，PD)能夠有效線性化放大器以提升功率效益。此外，當信號經過非線性放大器時，其輸出會有頻譜再生的現象，而造成鄰近通道的干擾。因此，線性化功率放大器降低位元錯誤率的同時，也必須能夠抑制頻譜再生。 在本篇論文中，將分析正交分頻多工系統在相加白高斯雜訊 (AWGN)下，使用預扭器來補償由功率放大器所引起的非線性失真，使之線性化。將使用到多項式(Polynomial)預扭器補償有記憶性的功率放大器，使用的是Wiener-Hammerstein PA。在補償的架構上，藉由使用Wiener-Hammerstein Model和其Inverse Model所組成，這樣可以簡化用查表法(Look-up Table，LUT)和其他補償方法，所帶來的複雜度問題。為了探討輸入平均功率對位元錯誤率之影響，利用接收端遞迴解碼估測(Iterative Decoder Estimation)，將操作在飽和後的非線性失真補償回來，使得功率放大器線性地操作在飽和區之內。本論文主要的架構是傳送端加上數位預扭器以及接收端加上遞迴解碼估測，結果證明能使功率放大器具有高功率效率，並能有效地克服非線性失真效應。[[abstract]]The orthogonal frequency division multiplex (OFDM) system has an advantage of high bandwidth efficiency, and is able to resist the multipath fading interference; its major disadvantage is high peak to average power ratio (PAPR). The signal passing a power amplifier (PA) can be clipped depending on the operation point of the PA. This clipped signal results in distortion. Baseband predistorter (PD) can efficiently linearize the power amplifier so as to improve the power efficiency. In addition, it can reduce the bit error rate and also suppress spectrum regrowth. In this thesis, we analyze the use of PD to compensate the nonlinear distortion caused by the PA in OFDM systems, which in AWGN. We use polynomial predistorter to compensate the memory PA, which is Wiener-Hammerstein PA. The compensate architecture is used by Wiener-Hammerstein model and its Inverse model. It can simplify the complexity problem that used Look-up Table (LUT) method and others’. To discus the impact for bit error rate which caused by input average power, uses iterative estimation to compensate the non-linear distortion on saturation area. Adds the digital predistorter on transmitter and adds the iterative estimation on receiver. The result is power amplifiers have high power efficiency, and it can overcome nonlinear effect effectively